/**
 * Copyright 2005 The Apache Software Foundation
 * <p>
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.mapred;

import java.io.IOException;

import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableComparable;

/**
 * Default {@link MapRunnable} implementation.
 */
public class MapRunner implements MapRunnable {
    private JobConf job;
    private Mapper mapper;
    private Class inputKeyClass;
    private Class inputValueClass;

    @Override
    public void configure(JobConf job) {
        this.job = job;
        this.mapper = (Mapper) job.newInstance(job.getMapperClass());
        this.inputKeyClass = job.getInputKeyClass();
        this.inputValueClass = job.getInputValueClass();
    }

    @Override
    public void run(RecordReader input, OutputCollector output,
                    Reporter reporter) throws IOException {
        try {
            // allocate key & value instances that are re-used for all entries
            WritableComparable key = (WritableComparable) job.newInstance(inputKeyClass);
            Writable value = (Writable) job.newInstance(inputValueClass);
            while (input.next(key, value)) {
                // map pair to output
                mapper.map(key, value, output, reporter);
            }
        } finally {
            mapper.close();
        }
    }

}
